This invention relates generally to gaseous fuel cells and is particularly directed to a current collecting electrode for use in a molten carbonate fuel cell.
A molten carbonate fuel cell converts the chemical energy of gasifier fuel gases directly into electricity without an intermediate conversion either to heat or to mechanical energy as in conventional power systems. The electrochemical fuel cell consists of two porous electrodes separated by an electrolyte contained within a porous matrix. Up to several hundred of these single-cell units can be assembled using sheet metal bipolar plates to form any size stack desired. The individual cells function as separate batteries coupled in series to provide an
This type of energy source is referred to as a molten carbonate fuel cell because the electrolyte is in the form of a liquid at typical cell operating temperatures in the range of 550.degree. C. to 750.degree. C. The electrolyte is generally mixed so as to form a matrix with an inert particulate material which remains solid during cell operation to maintain spacing between the electrodes. Most molten carbonate fuel cell electrolytes are ternary or binary mixtures of, for example, lithium carbonate, potassium carbonate, and sodium carbonate. Anode electrodes for these cells may be, for example, nickel-, cobalt- or chromium-containing alloys. The cathode electrode is typically comprised of silver or nickel. A fuel gas consisting primarily of H.sub.2 and CO is provided to the anode/electrolyte interface, with the H.sub.2 and CO converted to H.sub.2 O and CO.sub.2, respectively, releasing electrons that are transferred via an external circuit to the cathode. At the porous lithiated nickel oxide cathode, oxidant gases consisting of CO.sub.2 and O.sub.2 combine with the anodically produced electrons to form carbonate ions CO.sub.3.sup.2-. The ion thus produced is then transferred from the cathode through the electrolyte to the anode in completing the reaction circuit, at which point the carbonate ion is available to react with the H.sub.2 and/or CO fuel gas.
The catalyst is typically comprised of a ceramic conducting material such as a perovskite containing lanthanum, strontium, cobalt or nickel having properties making it suitable for use as a catalyst in low temperature aqueous electrolyte cells, molten carbonate electrolyte and high temperature solid electrolyte cells. In operation, the fuel and oxidant gases are directed via a plurality of gas channels into contact with the anode and cathode catalysts where they react as previously described. Structural problems caused primarily by corrosion and dissolution of the various materials in the fuel cell have limited the commercial attractiveness of these power sources. For example, earlier approaches making use of sintered catalysts encountered problems with the corrosion and dissolution of the perovskite utilized therein. In addition, because it was generally required that the catalyst be comprised of a sinterable material, many nonsinterable particulates were eliminated as catalysts in gaseous fuel cells in spite of the fact that their electrical properties were highly desirable for such applications. In some cases, a nonsinterable particulate typically in powder form was incorporated in a molten carbonate fuel cell by providing a perforated plate between the current collecting element and the catalyst. However, this increases the complexity and cost of fuel cell fabrication, particularly where large numbers of single-cell units are assembled in a stacked arrangement to form a large molten carbonate stacked fuel cell.
The present invention is intended to overcome the aforementioned limitations of the prior art by providing an integrated current collecting electrode with a catalyst support for use in a molten carbonate fuel cell. The integrated electrode arrangement of the present invention maintains catalyst-current collector separation while providing efficient reactant gas distribution to the catalyst.